1. Field of the Invention
This invention relates to methods for forming silicon oxide dielectric isolation layers in integrated circuit devices by thermal oxidation of silicon. More particularly, the invention relates to methods of dry oxidation of silicon to form high purity silicon oxide dielectric field oxide isolation layers.
2. Description of the Related Art
Microelectronics fabrication of integrated circuits is commonly done employing silicon semiconductor substrates and silicon semiconductor layers formed on those substrates to form the components of the integrated circuit microelectronics fabrication. The dielectric isolation of portions of the silicon substrate area is achieved by a thick silicon oxide dielectric layer called a field oxide (FOX) isolation layer. The formation of the field oxide (FOX) isolation layer is accomplished by the method of local oxidation of silicon (LOCOS), whereby a portion of a silicon device area is protected from oxidation by a layer of silicon nitride impervious to an oxidant species, while forming the silicon oxide dielectric field oxide (FOX) isolation layer in the region adjacent to the protected area. Subsequently, the silicon nitride masking layer is removed and generally replaced by another silicon oxide dielectric layer, usually thinner than the silicon oxide dielectric field oxide (FOX) isolation layer, also formed by thermal oxidation of silicon.
The silicon substrate area wherein there has not been formed a thick silicon oxide field oxide (FOX) isolation layer is the region in which active devices are to be located. A typical active device is the field effect transistor (FET) device, in which a thin silicon oxide dielectric layer serves as the gate oxide insulation layer upon the silicon substrate in the active device area between the silicon substrate channel region and the polysilicon gate electrode layer. The region where the relatively thick field oxide (FOX) isolation layer adjoins the much thinner silicon oxide gate oxide insulation layer underneath the gate electrode exhibits a characteristic appearance known as a xe2x80x9cbird""s beakxe2x80x9d and is a region of considerable interaction of physical stresses and chemical interactions due to the different material phases intimately involved.
The formation of silicon oxide dielectric field oxide (FOX) isolation layers and silicon oxide dielectric gate oxide insulation layers by thermal oxidation of silicon employing silicon nitride layers for selective masking, although satisfactory in general is not without problems in the art of integrated circuit microelectronics fabrication. In particular, the formation of silicon oxide layers of optimal purity so that foreign phases and contaminant ionic species are minimized is difficult because of the very long oxidation times typically required to form the thick silicon oxide layers required. The formation of heterogeneous foreign phases in the xe2x80x9cbird""s beakxe2x80x9d region in the silicon oxide dielectric field oxide (FOX) isolation layer adjacent to the original silicon nitride masking layer and now adjacent to the gate oxide layer may concentrate stresses in the otherwise homogeneous silicon oxide dielectric material. This may lead to excessive local etching when attempting to remove the residual phases, resulting in yield losses due to over-etching and in a microporous structure within the silicon oxide dielectric field oxide (FOX) isolation layer. Such a Inicroporous structure may retain deleterious process residues and foreign material, from the gate oxide and electrode formation material and process or the active region masking material and process.
Desirable in the art of integrated circuit microelectronics fabrication are methods for selective oxidation of silicon to form thick silicon oxide field oxide (FOX) isolation layers of silicon oxide dielectric material without inhomogeneities of composition or structure, particularly at interfaces and adjacencies with other portions of the device structure.
Various methods have been disclosed for forming silicon oxide layers for isolating regions of semiconductor substrates within microelectronics fabrications.
For example, Liu et al., in U.S. Pat. No. 5,151,381, disclose a method for forming field isolation silicon oxide layers which reduces or eliminates localized defects known as ribbons. The method employs dry thermal oxidation of silicon at a first temperature less than 1050 degrees centigrade, followed by an oxidation step at a second temperature greater than 1050 degrees centigrade, whereby flow of the field silicon oxide material ensues, thereby reducing stresses compared to conventional oxidation temperatures below 1000 degrees centigrade.
Further, Hsue et al., in U.S. Pat. No. 5,554,560, disclose a method for forming planar silicon oxide field oxide (FOX) isolation layers with improved resistance to formation of localized stringer defects. The method employs local oxidation of silicon with silicon nitride selective masking, and employs a sacrificial layer of spin-on-glass (SOG) dielectric material or anti-reflective coating (ARC) dielectric material to enable the resulting surface of the isolation layer to be more planar by etching back.
Still further, Lee, in U.S. Pat. No. 5,686,344, discloses a method for forming silicon oxide dielectric isolation regions within a silicon substrate in both the device isolation and well regions separating different polarities of silicon. The method employs thermal oxidation of silicon in an environment of O2/H2 at temperatures between 900 and 1000 degrees centigrade to form thick silicon oxide field oxide isolation layers between device wells and silicon oxide dielectric isolation layer within the device well.
Desirable within the art of integrated circuit microelectronics fabrication are additional methods and materials which may be employed for forming field isolation dielectric layers employing thermal oxidation of silicon within which impurity phases, inhomogeneities and defects causing stresses within the integrated circuit microelectronics fabrication are reduced.
It is towards the foregoing goal that the present invention is both generally and more specifically directed.
A first object of the present invention is to provide a method for forming within a silicon semiconductor substrate employed within an integrated circuit microelectronics fabrication a silicon oxide dielectric layer with minimal foreign inhomogeneities.
A second object of the present invention is to provide a method in accord with the first object of the present invention where there is formed a silicon oxide dielectric field oxide (FOX) isolation layer with minimal foreign inhomogeneities or foreign material employing local dry thermal oxidation of a silicon semiconductor substrate employed within an integrated circuit microelectronics fabrication.
A third object of the present invention is to provide a method in accord with the first object of the present invention or the second object of the present invention, where the method is readily commercially implemented.
In accord with the objects of the present invention, there is provided a method for forming within a semiconductor substrate employed within an integrated circuit microelectronics fabrication a silicon oxide dielectric layer with minimal inclusion of inhomogeneities of phase or composition or other defects which give rise to stresses within the fabrication. To practice the method of the present invention, there is provided a silicon semiconductor substrate employed within a microelectronics fabrication. There is formed upon the substrate a patterned layer of silicon nitride to define regions where there is to be local oxidation to form silicon oxide dielectric layers. Such silicon oxide dielectric layers may be employed to provide field oxide (FOX) dielectric layers for isolation of active device areas. There is then formed in those regions silicon oxide dielectric layers employed as field oxide (FOX) isolation layers by dry thermal oxidation of silicon first at an elevated temperature of at least about 1100 degrees centigrade, followed by optional further oxidation at a lower temperature, to provide a silicon oxide dielectric material essentially free of inhomogeneities of phase or composition which lead to stress within the fabrication upon subsequent fabrication processing.
The present invention provides a method for forming within a silicon semiconductor substrate employed within a microelectronics fabrication employing local dry thermal oxidation a silicon oxide dielectric layer with reduced inhomogeneities of phase or composition and defects which may lead to stresses within the fabrication. The objects are achieved by oxidation first at a temperature of at least about 1100 degrees centigrade or higher.
The present invention may be employed where the substrate is employed within a microelectronics fabrication where the microelectronics fabrication is selected from the group comprising integrated circuit microelectronics fabrications, charge coupled device microelectronics fabrications, solar sell microelectronics fabrications, ceramic substrate microelectronics fabrications and flat panel display microelectronics fabrications.
The method of the present invention employs materials and methods as are known in the art of integrated circuit microelectronics fabrication, but in ranges and sequences which are novel and not anticipated. Thus the method of the present invention is readily commercially implemented.